This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-333188, filed Oct. 30, 2001; No. 2001-333189, filed Oct. 30, 2001; and No. 2002-311454, filed Oct. 25, 2002, the entire contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a deflection yoke and a cathode-ray tube apparatus with the deflection yoke. In particular, this invention relates to a semitoroidal deflection yoke comprising a pair of saddle-shaped horizontal deflection coils with a substantially truncated-pyramidal shape; a magnetic core with a substantially truncated-conical shape; and a pair of vertical deflection coils with a toroidal shape, and also to a cathode-ray tube apparatus having this semitoroidal deflection yoke.
2. Description of the Related Art
At present, self-convergence type inline color cathode-ray tube apparatuses have widely been used. This type of cathode-ray tube apparatus includes an inline electron gun assembly that emits three inline electron beams traveling in a single plane, and a deflection yoke that produces a pincushion-shaped horizontal deflection magnetic field and a barrel-shaped vertical deflection magnetic field.
In this cathode-ray tube apparatus, the deflection yoke is a component that principally consumes electric power. In order to reduce the power consumption of the cathode-ray tube apparatus, it is necessary to reduce the power consumption of the deflection yoke. Besides, in these years, enhanced resolution and visibility have been required, and a high deflection frequency has been used in most cases. For example, in order to use this cathode-ray tube apparatus for a high-definition TV or a monitor of an OA apparatus such as a personal computer, the deflection frequency needs to be increased. However, when the deflection yoke is activated by such a high frequency, the deflection electric power increases and also the amount of heat emitted from the deflection yoke increases.
In general, the deflection electric power is reduced by decreasing the diameter of the neck of the envelope and the outside diameter of the yoke mount section, thereby making smaller the space for actions of the deflection magnetic fields and causing the deflection magnetic fields to efficiently act on electron beams. However, in the conventional cathode-ray tube apparatus, the electron beams travel in the vicinity of the inner surface of the yoke mount section. Thus, if the diameter of the neck or the outside diameter of the yoke mount section is further reduced, the electron beams may impinge on the inner surface of the yoke mount section before reaching the phosphor screen. For example, when the deflection angle of electron beams takes a maximum value, that is, when the electron beams are deflected toward a corner of the phosphor screen, the electron beams impinge on the inner surface of the yoke mount section and an area on which no electron beams arrive will occur on the phosphor screen. Furthermore, if the electron beams continue to impinge on the inner surface of the yoke mount section, the temperature of the inner surface rises and there is a possibility of implosion of the vacuum envelope. In the conventional cathode-ray tube apparatus, it is thus difficult to further reduce the diameter of the neck or the outside diameter of the yoke mount section, thereby decreasing the deflection electric power.
As a solution to this problem, there is a proposal to form the yoke mount section in such a shape as to vary gradually from a circular shape on the neck side to a substantially rectangular shape on the panel side. This solution is based on the idea that when a rectangular raster is described on the phosphor screen, the region of passage of electron beams within the yoke mount section also becomes substantially rectangular.
If the yoke mount section is formed in a substantially truncated-pyramidal shape, according to the above proposal, it is possible to reduce the diameters of the yoke mount section in the major axis (horizontal axis) direction and minor axis (vertical axis) direction, while preventing the electron beams deflected toward the corner of the phosphor screen from impinging on the inner surface of the yoke mount section. Thus, by forming the horizontal deflection coils, vertical deflection coils and magnetic core in truncated-pyramidal shapes, the horizontal deflection coils and vertical deflection coils are disposed closer to the region where the electron beams travel. Accordingly, the electron beams can efficiently be deflected and the deflection electric power can be reduced.
On the other hand, there are various types of deflection yokes. For instance, there are a saddle/saddle type deflection yoke having saddle-shaped horizontal and vertical deflection coils, and a semitoroidal deflection yoke having a combination of a saddle-shaped horizontal deflection coil and a toroidal vertical deflection coil.
The saddle/saddle type deflection yoke comprises a pair of truncated-pyramidal saddle-shaped horizontal deflection coils disposed on the inside of a separator; a pair of truncated-pyramidal saddle-shaped vertical deflection coils disposed on the outside of the separator; and a truncated-pyramidal magnetic core covering the vertical deflection coils (see, for instance, Jpn. Pat. Appln. KOKAI Publication No. 11-265666).
In the above-described saddle/saddle type deflection coils, compared to the semitoroidal deflection coils, the deflection electric power can be reduced. However, it is difficult to manufacture the truncated-pyramidal magnetic core with high precision. It is also difficult to wind the vertical deflection coils around the truncated-pyramidal magnetic core in a toroidal fashion. Consequently, the manufacturing cost of the deflection yoke increases, and a general-purpose use is difficult to achieve.
Furthermore, the saddle/saddle type deflection coils have a small space for radiation of heat emitted from the horizontal deflection coils and vertical deflection coils, and the temperature of the deflection yoke may rise. In these years, in accordance with the modern trend toward flattening of the outer surface shape of the panel, the inner surface shape of the panel has also become flattened more and more. To meet the trend, if design is made to correct a pincushion type distortion in the vertical direction of the screen and to make it substantially linear at the peripheral areas, the vertical pincushion type distortion near an intermediate area in the vertical direction may remain in some cases. This may degrade the quality of display images.
The present invention has been made in consideration of the above problems, and its object is to provide a deflection yoke with reduced deflection electric power, manufacturing cost and heat emission amount, and with an enhanced quality of a display image on the screen, and to also provide a cathode-ray tube apparatus having this deflection yoke.
According to a first aspect of the invention, there is provided a deflection yoke comprising:
a pair of saddle-shaped horizontal deflection coils disposed to be symmetric with respect to a center axis and having a substantially truncated-pyramidal shape;
a magnetic core having a substantially truncated-conical shape and disposed coaxially with the center axis on an outer peripheral side of the horizontal deflection coils; and
a pair of toroidal vertical deflection coils disposed to be symmetric with respect to the center axis,
wherein a middle point of an entire length along the center axis from a large-diameter portion to a small-diameter portion of the magnetic core lies on a small-diameter portion side of the horizontal deflection coil relative to a point lying at a distance of 0.41xc3x97HL along the center axis from a large-diameter portion of the horizontal deflection coil, where HL is an entire length of the horizontal deflection coil along the center axis.
According to a second aspect of the invention, there is provided a cathode-ray tube apparatus comprising: a vacuum envelope having a panel with a phosphor screen disposed on an inside of the panel, a funnel formed continuous with the panel, and a cylindrical neck formed continuous with a small-diameter end portion of the funnel;
an electron gun assembly disposed within the neck and emitting electron beams toward the phosphor screen; and
a deflection yoke mounted on an outside of the vacuum envelope and producing deflection magnetic fields for deflecting the electron beams emitted from the electron gun assembly in horizontal and vertical directions,
wherein the deflection yoke comprises:
a pair of saddle-shaped horizontal deflection coils disposed to be symmetric with respect to a tube axis and having a substantially truncated-pyramidal shape;
a magnetic core having a substantially truncated-conical shape and disposed coaxially with the tube axis on an outer peripheral side of the horizontal deflection coils; and
a pair of toroidal vertical deflection coils disposed to be symmetric with respect to the tube axis,
wherein a middle point of an entire length along the tube axis from a large-diameter portion to a small-diameter portion of the magnetic core lies on a small-diameter portion side of the horizontal deflection coil relative to a point lying at a distance of 0.41xc3x97HL along the tube axis from a large-diameter portion of the horizontal deflection coil, where HL is an entire length of the horizontal deflection coil along the tube axis.